1. Field of the Invention
The present invention relates to a method for removing detrimental chemical impurities adhered to substrates to maintain necessary high cleanliness, and to a box for accommodating the substrates to store and transfer. The substrates include ones such as semiconductor wafers that are between processing machines in manufacturing semiconductor devices, substrates on which LCD pattern is formed, substrates for photo-masking, and magnetic discs.
2. Discussion of the Background
As semiconductor devices become finer- and denser-packed, processing becomes more complicated. As a result, adverse affects of contamination due to gaseous impurities generated in the process become conspicuous. For instance, in the dry etching process or the CVD (Chemical Vapor Deposition) process for metallic wiring, acid gases of high vapor pressure such as chlorine (Cl) and fluorine (F) compounds remain on semiconductor wafers to corrode the metallic wiring on the semiconductor wafers. Further, in the deep-UV lithography processes, basic gases such as ammonia or the like in the atmosphere or adsorbed by the semiconductor wafers cause an abnormality of pattern in machining the resist. These adverse influences due to the gaseous impurities on process performance cause problems.
In the existing manufacturing method of semiconductor devices, to secure and maintain cleanliness of the atmosphere in a clean room in which the semiconductor wafers are processed, a gaseous impurity-trapping filter such as a chemical filter or activated carbon filter is provided to an air conditioner to trap and remove efficiently these detrimental gaseous impurities. By employing such a method, the detrimental gaseous impurities in the process are prevented from causing contamination.
However, when transferring semiconductor wafers from one processing machine to another processing machine or from one room to another room in a clean room, and from one machine to another machine laid between clean rooms, as a clean space isolated from the space inside or outside the clean room, hermetically sealed boxes are in use. Accordingly, when transferring wafers from one process to another process, in the hermetically sealed box, due to out gases from the wafers, concentrations of these gaseous impurities become high. As a result, these gaseous impurities brought in by the wafers themselves contaminate the clean room.
Japanese Patent Application No. HEI 6-87964 discloses a method for cleanly isolating semiconductor wafers from contaminated space outside a clean room. In the method, semiconductor wafers are accommodated in a box of which atmosphere is the same with that of the clean room, and the box is transferred from a clean room to another clean room.
In the box constituted for the inside thereof to communicate with the outside atmosphere, a particle-trapping HEPA (High Efficiency Particle Air) filter or ULPA (Ultra Low Penetration Air) filter and a gaseous impurity-trapping chemical filter are disposed. In the box, semiconductor wafers and substrates for LCD, which are objects to be processed, are accommodated and transferred. However, in this method, the chemical filter filters the atmosphere always containing impurities to supply into the box. Accordingly, there is a problem that the chemical filter has very short life.
Further, Japanese Patent Laid-open Publication (KOKAI) No. HEI 8-148551 discloses a hermetically sealed case for accommodating substrates that is provided with filters that trap gaseous impurities at a gas inlet and outlet where the atmospheric gas goes in and out. However, the flow rate of the gas in the atmosphere, being restricted to approximately 1 1/min, is impractical. For instance, when a volume of 23 1 of a box for 8-inch wafer is replaced by the atmospheric gas to trap impurities, under such a flow rate, more than 20 min is required. Accordingly, impurities that are brought in the box from the external atmosphere during opening/closing to insert the wafers are adhered to the wafers. The impurity gas, being a base such as ammonia, is adsorbed by resist on the surface of the wafer to react to the resist, and being an acid such as sulfur oxide and chlorine, is absorbed by metallic wiring on the surface of the wafer to corrode the metallic wiring.